Light-emitting diode driving device and short protection method for driving device

ABSTRACT

A light-emitting diode (LED) driving device and a short protection method for a driving device are provided. The driving device includes an LED module, a driving circuit, a reference voltage setting circuit, a voltage comparison circuit, and a power supply. A first node of the LED module receives a lighting voltage, and a second node of the LED module has a first voltage. The reference voltage setting circuit receives the lighting voltage to generate a reference voltage. The voltage comparison circuit determines whether the first voltage is greater than the reference voltage when the LED module is turned off. When the first voltage is greater than the reference voltage, the voltage comparison circuit generates a short signal. The power supply supplies power to the LED module and determines whether to shut down the power of the LED driving device according to the short signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 105126183, filed on Aug. 17, 2016. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

FIELD OF THE INVENTION

The invention relates to a driving technology of a light-emitting diode(LED); more particularly, the invention relates to an LED driving deviceand a short protection method of a driving device.

DESCRIPTION OF RELATED ART

With the progress in semiconductor technology, brightness of an LED anda light-emitting efficiency thereof continuously increase. The LED hasadvantages of long service life, small volume, low consumption ofelectricity, low degree of pollution, great reliability, adaptation ofmass production, and so on. The LED can be extensively applied invarious fields, such as in illumination apparatuses, liquid crystaldisplays (LCD), backlight sources of large billboards, etc.

Generally, to prevent the collateral damages to crucial parts (e.g.,transistors) in a driving device when the LED is damaged, precautionarymeasures are often established to comply with the issue of short LED. Inanother aspect, the driving device of the LED often drives the LEDthrough scanning backlight, over driving, or local dimming according topulse width modulation (PWM) signals. Said driving device often changesthe cycle of electric current flowing through the LED and the amplitudeof the electric current, such that the bias of the LED in an on stagebecomes unstable. Thereby, if the LED is turned on, a short detectioncircuit in the driving device may malfunction. As such, manufacturersintend to direct the research and development activities to effectuateshort protection mechanism of the LED.

SUMMARY OF THE INVENTION

The invention provides an LED driving device and a short detectionmethod of an LED, so as to effectively prevent the driving device frombeing damaged by an LED encountering a short issue.

In an embodiment of the invention, a driving device including an LEDmodule, a driving circuit, a reference voltage setting circuit, avoltage comparison circuit, and a power supply is provided. A first nodeof the LED module receives a lighting voltage, and a second node of theLED module has a first voltage. The driving circuit is configured todrive the LED module. The reference voltage setting circuit receives thelighting voltage to generate a reference voltage. The voltage comparisoncircuit determines whether the first voltage is greater than thereference voltage when the LED module is turned off. When the firstvoltage is greater than the reference voltage, the voltage comparisoncircuit generates a short signal. The power supply is configured tosupply power to the LED module and determine whether to shut down thepower of the LED driving device according to the short signal.

In an embodiment of the invention, a short protection method of adriving device includes following steps. A first voltage of an LEDmodule is received. Here, a first node of the LED module receives alighting voltage, and a second node of the LED module has a firstvoltage. A reference voltage is generated. Here, the reference voltageis relevant to a breakdown voltage of a Zener diode and the lightingvoltage. Whether the first voltage is greater than the reference voltageis determined when the LED module is turned off, so as to generate ashort signal. Whether to shut down power of the LED driving device isdetermined according to the short signal.

In view of the above, the LED driving device and the short protectionmethod of the driving device generate the reference voltage through theZener diode, and the bias and the reference voltage of the LED moduleare applied to determine whether some of the LEDs in the LED moduleencounter the issue of short circuit, so as to shut down the power ofthe driving device. As such, the LED driving device provided herein caneffectively prevent the driving device from being damaged by the LEDencountering the short issue.

To make the above features and advantages of the invention morecomprehensible, several embodiments accompanied with drawings aredescribed in detail as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure, and are incorporated in and constitutea part of this specification. The drawings illustrate exemplaryembodiments of the disclosure and, together with the description, serveto explain the principles of the disclosure.

FIG. 1 is a schematic diagram of an LED driving device according to anembodiment of the invention.

FIG. 2 is a detailed circuit diagram of an LED driving device accordingto an embodiment of the invention.

FIG. 3 is a flowchart of a short protection method of a driving deviceaccording to an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic diagram of an LED driving device 100 according toan embodiment of the invention. With reference to FIG. 1, the LEDdriving device (hereinafter referred to as “driving device 100”)includes LED modules 110-1-110-4, a driving circuit 120, a referencevoltage setting circuit 130, a voltage comparison circuit 140, and apower supply 150. The driving device 100 may include one or more LEDmodules. In the present embodiment, four LED modules 110-1-110-4 areexemplified to explain the invention. People may adjust the requirednumber of LED modules (e.g., eight or more LED modules) in view of thepresent embodiment according to actual needs.

Each of the LED modules 110-1-110-4 includes a plurality of seriallyconnected LEDs. That is, each of the LED modules 110-1-110-4 includes aLED light string (i.e., a LED light bar) constituted by seriallyconnected LEDs. In the LED modules 110-1-110-4 described in the presentembodiment, each LED light string is comprised of six serially connectedLEDs, and people may adjust the number of LEDs in each LED light stringin view of the present embodiment according to actual needs. In theexemplary LED module 110-1, an anode terminal of the first LED LD1 inthe LED modules 110-1-110-4 serves as the first node N11 of the LEDmodules 110-1-110-4, so as to receive the lighting voltage VL suppliedby the power supply 150. A cathode terminal of the last LED LD6 in theLED module 110-1 serves as the second node N12 that is coupled to thedriving circuit 120. In the present embodiment of the invention, thesecond nodes N12-N42 of the LED modules 110-1-110-4 respectively includecorresponding first voltages V12-V42.

The driving circuit 120 is configured to drive the LED modules110-1-110-4. Specifically, the driving circuit 120 includes an LEDdriver 122 and current balancing switches 171-174 corresponding to theLED modules 110-1-110-4. The LED driver 122 can generate driving signalsSd1-Sd4 for controlling the current balancing switches 171-174. In otherwords, the LED driver 122 drives the LED modules 110-1-110-4 accordingto the driving signals Sd1-Sd4 by using the current balancing switches171-174. First terminals of the current balancing switches 171-174 arerespectively coupled to the corresponding LED modules 110-1-110-4,second terminals of the current balancing switches 171-174 arerespectively coupled to resistors R21-R24, and control terminals of thecurrent balancing switches 171-174 respectively receive thecorresponding driving signals Sd1-Sd4. The driving signals Sd1-Sd4 maybe PWM signals. The current balancing switches 171-174 may beimplemented in form of metal oxide semiconductor field effecttransistors (MOSFETs), e.g., n-type MOSFETs. If the first voltagesV12-V42 are overly large, the MOSFETs acting as the current balancingswitches 171-174 may be damaged accordingly.

The reference voltage setting circuit 130 is configured to receive thelighting voltage VL to generate a reference voltage Vref. The voltagecomparison circuit 140 selects the maximum first voltage from the firstvoltages V12-V12; on the condition that the LED modules 110-1-110-4 arebeing turned off, the voltage comparison circuit 140 determines whetherthe maximum first voltage is greater than the reference voltage Vref. Ifthe maximum first voltage is less than the reference voltage Vref, itindicates that no short issue occurs in the LEDs of the LED modules110-1-110-4. However, if some LEDs are damaged and thus result in theshort issue, the first voltages of the LED modules having the damagedLEDs are raised. The LEDs are diodes. Hence, if the voltage differenceat two ends of the LEDs are overly large, the LEDs are likely to bebroken down, and the two ends may be electrically conducted, such thatthe short issue occurs. Hence, if the maximum first voltage selectedfrom the first voltages V12-V42 is greater than the reference voltageVref, the voltage comparison circuit 140 generates a short signal SC.The power supply 150 receives an input voltage Vin to supply power (orsupply the lighting voltage VL) to the LED modules 1101-110-4;similarly, the power supply 150 also supplies power to the entire LEDdriving device 100. According to whether the short signal SC is beingenabled or not, the power supply 150 determines whether to shut down thepower of the LED driving device 100. That is, when the short signal SCis being enabled, the power supply 150 shuts down the power of the LEDdriving device 100.

The reasons of the increase in the first voltage when some of the LEDsin the LED modules encounter the short issue are described hereinafter.If the LED modules 110-1-110-4 already receive the lighting voltage VLbut are turned off due to the control of the LED driver 122 (e.g., thecontrol of the driving signal to stop the electric current from flowingthrough the LED modules 110-1-110-4, where the electric current isgenerated by the lighting voltage VL), and if each LED in the LED module110-1 remains intact, the first voltage V12 is obtained by subtractingsix LED biases from the lighting voltage VL. By contrast, if the LED LD1in the LED module 110-1 is damaged and thus becomes short, the firstvoltage V12 is obtained by subtracting five LED biases from the lightingvoltage VL. That is, as long as any LED in the LED modules is damagedand thus becomes short, the first voltage V12 is increased by one LEDbias in comparison with the original first voltage V12. When the LEDmodules 110-1-110-4 are being turned on, the electric current flowingthrough the LEDs does not remain constant, and thus the bias of each LEDmay float. Thereby, the step of “comparing the maximum voltage of thefirst voltages V12-V42 with the reference voltage Vref to determinewhether the LED encounters the short issue” may not be substantiallyfeasible. Hence, according to the present embodiment, the voltagecomparison circuit 140 performs the voltage comparison action on thecondition that the LED modules are electrically conducted and are beingturned off.

FIG. 2 is a detailed circuit diagram of the LED driving device 100according to an embodiment of the invention. In FIG. 2, the power supply150 is implemented in form of a direct-current-to-direct-current(DC-to-DC) converter 210 which receives the input voltage Vin togenerate the lighting voltage VL and determines whether to shut down thepower of the LED driving device 100 according to whether the shortsignal SC is being enabled or not.

The reference voltage setting circuit 130 includes a Zener diode ZD1 anda first resistor R1. The Zener diode ZD1 has a breakdown voltage. Acathode terminal of the Zener diode ZD1 receives the lighting voltageVL. The first resistor R1 is coupled between an anode terminal of theZener diode ZD1 and a ground terminal. Hence, when the Zener diode ZD isin a breakdown state, the reverse bias of the Zener diode ZD becomes aconstant breakdown voltage, such that the reference voltage Vref isobtained by subtracting the breakdown voltage in the Zener diode ZD1from the lighting voltage VL. Therefore, the lighting voltage VL shouldbe greater than the breakdown voltage; as such, when the electriccurrent flowing through the LED modules 110-1-110-4 is zero, the Zenerdiode ZD1 is in the breakdown state, and thereby the reference voltagesetting circuit 130 can operate smoothly.

The voltage comparison circuit 140 includes a photo coupler 220, a resetIC 230, and a power control switch 240. The voltage comparison circuit140 further includes a propagation circuit 250. The propagation circuit250 includes first diodes D1-D4 respectively corresponding to the LEDmodules 110-1-110-4. Anode terminals of the first diodes D1-D4 arecoupled to the first nodes N12-N42 of the LED modules 110-1-110-4 toreceive the first voltages V12-V42. Cathode terminals of the firstdiodes D1-D4 are coupled to the first input terminals NL1 of the photocoupler 270. Through the first diodes D1-D4, the voltage at the firstinput terminal NL1 of the photo coupler 270 is the maximum voltage amongthe first voltages V12-V42.

The first input terminal NL1 of the photo coupler 220 at the LED sidereceives the maximum voltage among the first voltages V12-V42 throughthe propagation circuit 250. The second input terminal NL2 of the photocoupler 220 at the LED side is coupled to the reference voltage settingcircuit 130 to receive the reference voltage Vref. The third terminal N3of the photo coupler 220 is coupled to the ground terminal, and thefourth terminal N4 (i.e., the output terminal) of the photo coupler 220generates the comparison signal SS. Thereby, the photo coupler 220 mayserve as the comparator and the isolator of the reference voltage Vrefand the maximum voltage among the first voltages V12-V42.

If each LED in the LED module 110-1 remains intact, the first voltageV12 is obtained by subtracting six LED biases from the lighting voltageVL. Given that the bias of each intact LED is 2.5V, the bias of thefirst diode D1 is 0.6V, the breakdown voltage of the Zener diode ZD1 isset as 16V, and the bias of the LED in the photo coupler 220 is set as1.2V. Thereby, the voltage at the first input terminal NL1 of the photocoupler 220 at the LED side is obtained by “subtracting six LED biases(6*2.5V=15V) and the bias (0.6V) of the first diode from the lightingvoltage VL”, and the reference voltage Vref is obtained by “subtractingthe breakdown voltage (16V) from the lighting voltage VL”. At this time,the difference between the first voltage (VL-6*2.5V-0.6V) at the firstinput terminal NL1 of the LED in the photo coupler 220 and the referencevoltage (VL-16V) at the second input terminal NL2 is not greater thanthe bias (1.2V) of the LED in the photo coupler 220; therefore, the LEDin the photo coupler 220 is not turned on, and the comparison signal SSremains disabled. By contrast, if the first LED LD1 in the LED module110-1 is damaged and thus encounters the short issue, and the other LEDsremain intact, the difference between the first voltage (VL-6*2.5V-0.6V)at the first input terminal NL1 of the LED in the photo coupler 220 andthe reference voltage (VL-16V) at the second input terminal NL2 isgreater than the bias (1.2V) of the LED in the photo coupler 220; hence,the LED in the photo coupler 220 is turned on, and the comparison signalSS becomes enabled.

The breakdown voltage of the Zener diode ZD1 provided herein may bedetermined by those who actually implement the present embodiment. Ifthe transistors in the driving device 100 have high tolerance, i.e., ifthe number of the LEDs encountering the short issue is somehowsignificant but the transistors can still remain intact, the breakdownvoltage in the Zener diode ZD1 can be set to have a small value. If,however, the transistors in the driving device 100 have low tolerance,i.e., if the number of the LEDs encountering the short issue is somehowinsignificant but the transistors may still be easily damaged, thebreakdown voltage in the Zener diode ZD1 should be set to have a largevalue. The breakdown voltage may be properly adjusted according to thetolerance of the transistors. It should be mentioned that the breakdownvoltage cannot be greater than the sum of the total LED biases of allLEDs (e.g., six LEDs) in the LED light string, the bias of one diode(e.g., the diode D1), and the bias of the LED in the photo coupler 220.

The comparison signal SS is sent to the reset IC 230 through the fourthterminal N4 of the photo coupler 220. Specifically, in some embodimentsof the invention, the LED scanning frequency generated through thedriving signals Sd1-Sd4 by the LED driver 122 is relatively high (e.g.,480 Hz); thus, the cycle time of the comparison signal SS generated bythe photo coupler 222 is thus overly short, and the voltage level of thecomparison signal SS becomes inaccurate. The reset IC 230 serves toadjust the voltage level and the cycle time of the comparison signal SSand ensures said cycle time to be greater than 200 msc, such that thetransistor M1 can operate smoothly. The VCC terminal of the reset IC 230is connected to the system voltage Vdd, the GND terminal is coupled tothe ground terminal, and the RESET terminal generates the comparisonsignal SS whose voltage level has been adjusted.

The control terminal of the power control switch 240 receives thecomparison signal SS. When the maximum first voltage among the firstvoltages V12-V42 is greater than the reference voltage Vref, the powercontrol switch enables the short signal SC. Specifically, the powercontrol switch 240 includes a transistor M1 (e.g., a p-type enhancedMOSFET). A gate terminal of the transistor M1 is the control terminal ofthe power control switch 240. A first terminal of the transistor M1generates the short signal SC, and a second terminal of the transistorM1 is coupled to the ground terminal. Hence, when the comparison signalSS is being enabled (i.e., logic “0”), the first terminal and the secondterminal of the transistor M1 are electrically conducted, so as toenable the short signal SC (i.e., logic “0”). The power supply 150 shutsdown the power of the LED driving device 100 when the short signal SC isenabled.

FIG. 3 is a flowchart of a short protection method of a driving deviceaccording to an embodiment of the invention. The short protection methodprovided herein is adapted to the LED driving device 100 depicted inFIG. 1. With reference to FIG. 1 and FIG. 3, in step S310, the voltagecomparison circuit 140 receives the first voltages V12-V42 of the LEDmodules 110-1-110-4. First nodes of the LED modules 110-1-110-4 receivethe lighting voltage VL, and second nodes N12-N42 of the LED modules110-1-110-4 have the first voltages V12-V42. In step S320, the referencevoltage setting circuit 130 generates the reference voltage Vref. Here,the reference voltage Vref is relevant to the breakdown voltage of theZener diode ZD1 and the lighting voltage VL. In step S330, the voltagecomparison circuit 140 determines whether the first voltage is greaterthan the reference voltage Vref when the LED modules 110-1-110-4 turnedoff, so as to generate a short signal SC. If there is only one LEDmodule, there would be only one first voltage. If there are plural LEDmodules, the maximum first voltage is selected from the first voltagesand then compared with the reference voltage Vref. In step S340, thepower supply 150 determines whether to shut down power of the LEDdriving device 100 according to the short signal SC. The detailed stepsof the short protection method and the hardware applied in the methodare explained in the previous embodiments.

To sum up, in the LED driving device and the short protection method ofthe driving device provided herein, the Zener diode is applied togenerate the reference voltage, and the bias in the LED module and thereference voltage are applied to determine whether any of the LEDs inthe LED module encounter the short issue, so as to shut down the powerto the driving device. As such, the LED driving device provided hereincan effectively prevent the driving device from being damaged by the LEDencountering the short issue.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed embodimentswithout departing from the scope or spirit of the invention. In view ofthe foregoing, it is intended that the invention covers modificationsand variations of this disclosure provided that they fall within thescope of the following claims and their equivalents.

What is claimed is:
 1. A light-emitting diode driving device comprising:a light-emitting diode module, a first node of the light-emitting diodemodule receiving a lighting voltage, a second node of the light-emittingdiode module having a first voltage; a driving circuit configured todrive the light-emitting diode module; a reference voltage settingcircuit receiving the lighting voltage to generate a reference voltage;a voltage comparison circuit determining whether the first voltage isgreater than the reference voltage when the light-emitting diode moduleis turned off and generating a short signal when the first voltage isgreater than the reference voltage; and a power supply configured tosupply power to the light-emitting diode module and determine whether toshut down the power of the light-emitting diode driving device accordingto the short signal, wherein the voltage comparison circuit comprises: aphoto coupler, wherein a first input terminal of the photo couplerreceives the first voltage, a second input terminal of the photo coupleris coupled to the reference voltage setting circuit to receive thereference voltage, a third terminal of the photo coupler is coupled to aground terminal, and a fourth terminal of the photo coupler generates acomparison signal; a reset IC configured to adjust a voltage level ofthe comparison signal; and a power control switch, a control terminal ofthe power control switch receiving the comparison signal, the powercontrol switch enabling the short signal when the first voltage isgreater than the reference voltage, wherein the power supply shuts downthe power of the light-emitting diode driving device when the shortsignal is being enabled.
 2. The light-emitting diode driving deviceaccording to claim 1, wherein the light-emitting diode module comprisesa plurality of serially connected light-emitting diodes, an anodeterminal of a first light-emitting diode of the light-emitting diodes ofthe light-emitting diode module receives the lighting voltage, and acathode terminal of a last light-emitting diode of the light-emittingdiodes is the second node of the light-emitting diode module.
 3. Thelight-emitting diode driving device according to claim 1, wherein thereference voltage setting circuit comprises: a Zener diode having abreakdown voltage, a cathode terminal of the Zener diode receiving thelighting voltage; and a first resistor coupled between an anode terminalof the Zener diode and a ground terminal, wherein the reference voltageis obtained by subtracting the breakdown voltage from the lightingvoltage, and the lighting voltage is greater than the breakdown voltage.4. The light-emitting diode driving device according to claim 1, whereinthe power control switch comprises a transistor, a gate terminal of thetransistor is the control terminal of the power control switch, a firstterminal of the transistor generates the short signal, and a secondterminal of the transistor is coupled to the ground terminal.
 5. Thelight-emitting diode driving device according to claim 1, wherein thevoltage comparison circuit further comprises: a propagation circuitcomprising a first diode, an anode terminal of the first diode beingcoupled to the first node of the light-emitting diode module to receivethe first voltage, a cathode terminal of the first diode being coupledto the first input terminal of the photo coupler.
 6. The light-emittingdiode driving device according to claim 1, wherein the driving circuitcomprises: a light-emitting diode driver generating a driving signal;and a current balancing switch coupled to the light-emitting diodemodule, a control terminal of the current balancing switch receiving thedriving signal, wherein the light-emitting diode driver drives thelight-emitting diode module according to the driving signal by using thecurrent balancing switch.
 7. A short protection method of a drivingapparatus, comprising: receiving a first voltage of a light-emittingdiode module, a first node of the light-emitting diode module receivinga lighting voltage, a second node of the light-emitting diode modulehaving a first voltage; generating a reference voltage, wherein thereference voltage is relevant to a breakdown voltage of a Zener diodeand the lighting voltage; determining whether the first voltage isgreater than the reference voltage when the light-emitting diode moduleis turned off, so as to generate a short signal; and Whether to shutdown power of the LED driving device is determined according to theshort signal, wherein the step of determining whether the first voltageis greater than the reference voltage comprises: receiving the firstvoltage by a first input terminal of a photo coupler and receiving thereference voltage by a second input terminal of the photo coupler,wherein a third terminal of the photo coupler is coupled to a groundterminal, a fourth terminal of the photo coupler generates a comparisonsignal, and the power of the light-emitting diode module is shut downwhen the comparison signal is being enabled.
 8. The short protectionmethod according to claim 7, wherein the reference voltage is obtainedby subtracting the breakdown voltage from the lighting voltage, and thelighting voltage is greater than the breakdown voltage.